Switches in the low-voltage range with electromechanical trips are known for example as miniature circuit breakers. These interrupt the flowing current, for example when a predetermined current value is exceeded. The trip comprises a trip unit, which is formed as a latching solenoid (maglatch), which has a permanent magnet, a winding and a ferromagnetic push rod, the push rod being attracted by the magnetic field of the permanent magnet counter to the force of a spring. The tripping takes place by the winding that is arranged on the permanent magnet generating an opposing magnetic field, which compensates for the magnetic field of the permanent magnet in the region of the push rod in such a way that the push rod is displaced by the spring in the direction of its longitudinal axis to trip the switch. The push rod in this case interacts with a breaker mechanism, in which a breaker shaft is kept under mechanical prestress and unlatches the push rod. The breaker shaft rotating about its longitudinal axis separates the contact elements, and thus opens the switch.
For testing the latching solenoid, i.e. in particular the winding for wire rupture, it is known to send through the winding a steady-state test current that is too small to release the push rod. The test current is monitored, an interruption of the current particularly indicating a wire rupture.
A disadvantage of this is that the testing is relatively complex.